Production of synthetic structures



Patented Jan. 12, 1943 PRODUCTION OF SYNTHETIC STRUCTURES John B. Miles,Greenville, Dcl., assignor to E. I. du Pont dc Nemours & Company,Wilmington, Del., a corporation of Delaware No Drawing. Application May6, 1939, Serial No. 272,136

, 12 Claims. This invention relates to synthetic linear polymers, andparticularly to a process for improving the properties of shapedarticles prepared from fiber-forming synthetic linear polyamides.

This invention is concerned in particular with the new class offilament-forming materials known as synthetic linear polymers describedin U. S. Patents Nos. 2,071,250; 2,071,251; 2,071,252 and 2,071,253. Aindicated in these patents, a characteristic property of these polymersis their crystallinity and the fact that filaments and the like preparedfrom them can be cold drawn, whereupon they show molecular orientationalong the fiber axis. The cold drawn filaments are stronger and moreelastic than the undrawn' filaments and are therefore more useful in thepreparation of yarns and fabrics. Other articles prepared from thesepolymers; e. g., bristles, ribbons, sheets, and rods, are likewiseimproved by cold drawing, cold rolling or other processes which bringabout molecular orientation of the molecules.

A particularly useful subclass of filamentforming linear polymers isthat of the polyamides. These are of two types: those obtainable frompolymerizable monoaminomonocarboxylic acids and their amide-formingderivatives, including caprolactam, and those obtainable from thereaction of suitable diamines with suitable dibasic carboxylic acids ortheir amideforming derivatives. The latter type is more fully describedin U. S. Patent No. 2,130,948. In these polyamides theamide groups forman integral part of the main chain of atoms. The present invention willbe described with particular reference to the polyamides, although it isto be understood that it is not so limited.

In my applications, Serial Nos. 125,941 and 227,014 filed February 15,1937 and August 26, 1938, respectively, and in application Serial No.183,922 filed by V. R. Hardy and myself January 7, 1938, there isdisclosed the unusual setting effect of steam and hot water, and of hotliquids or vapors of organic non-solvent swelling agents for thepolyamide or polyamide articles, that is, permanently setting thearticles in a specially imposed form or shape to which they tend torecover after deformation.

- Such setting of articles comprising synthetic linear polymers, evenwhen held under a slight tension, results in shrinkage.

Textile yarns (including oriented polyamide yarns) may be shrunk(residual shrinkage removed) by a treatment of the yarns in the relaxedcondition with hot water. Such treatments are usually accomplished bysubjecting the yarn in skeins to the action of hot water whereupon theyarn decreases in length with anaccompanying decrease in residualshrinkageand increase in denier. This decrease in length of a textileyarn upon being subjected to a shrinkage treatment will be referred toas process shrinkage. This skein process is expensive as it mustnecessarily be discontinuous; likewise, the necessary v handling tendsto degrade the yarn. Such a process is particularly objectionable in thecase 'of polyamide yarns since they are spun directly from melt at veryhigh spinning speeds making possible efficientand rapid continuousproduction. Another disadvantage in such a process is the decrease inlength and increase in denier after shrinkage. This decrease in lengthand increase in denier may be non-uniform and is not easily controlled.

It is known to stretch textile filaments such as cellulosic rayon and tosubject them while in a stretched condition to the action of hot waterfollowed by drying, whereupon the dried yarn is obtained insubstantially the same dimensions- Such a condition, is, however,unstable, for upon being subsequently subjected to shrinking conditionsthe yarn shrinks and shows no permanent eifect of this interveningtreatment under tension. In fact, such processes are used to produceyarns of abnormally high shrinkage for special purposes.

It ha now been found that oriented synthetic linear polyamide filaments,sheets, and ribbons, as well as synthetic linear polyamide articles suchas yarns and woven fabrics constructed from such oriented filaments, andin which construction the linear dimensions of the filaments can berestrained from shrinkage (in knitted goods, for example, the lineardimensions of the filaments cannot be restrained from shrinkage), can Ibe set in their preshrunk dimensions by subjecting them to settingconditions while restraining the filaments, ribbons or yarns from anyreduction in linear dimensions, and in the case of ribbong and sheets,planar dimensions. These structures, when so treated, tend always toretain their set dimensions even though they are subsequently exposed ina relaxed state to conditions which would result in shrinkage ofpreviously unset structures. That is to say, the residual shrinkage ofsuch structures is materially reduced, if not substantially eliminated,without subjecting them to process shrinkage. Althougn of lessimportance, it has been found that a polyamide structure can actually bestretched to a material extent, for example, or more, and set in such astretched condition with a substantial reduction in residual shrinkage.

By the term residual shrinkage"'is meant the percentage decrease inlength which the filament or yarn undergoes when it is subjected in arelaxed condition to a hot aqueous treatment with or without detergentsat temperatures of 95-100 C. for five minutes. In determining residualshrinkage a measured sample is subjected to the shrinkage treatmentdescribed above and dried in a relaxed condition, whereupon its lengthis determined at the same humidity and tempera ture as the initialmeasurements and the percentage shrinkage calculated.

It is therefore an object of this invention to set structures comprisingoriented synthetic linear polyamide filaments, yarns, ribbons, sheets orthe like while restrainingthe filaments, yarns, ribbons, sheets or thelike from' any substantial reduction in linear dimensions, and in thecase of ribbons and sheets, planar dimensions.

It is a further object of this invention'to provide a, process forreducing the residual shrinkage of oriented polyamide articles withoutallowing them to shrink.

A further object of this invention is the reduction of the residualshrinkage of oriented polyamide filaments, yarns and the like while theyare maintained in such a manner that theycannot freely change theirlinear dimensions.

Another object of this invention is the provision of a continuous methodfor removing the residual shrinkage of oriented polyamide filamentswithout accompanying shrinkage.

Other objects of this invention will hereinafter become apparent.

The objects of this invention are accomplished, in general, by settingstructures comprising oriented synthetic linear polyamide filaments,yarns, ribbons, sheets or the like by a treatment at elevatedtemperatures with hydroxylated or non-hydroxylated, non-solvent swellingagents for the polyamide while restraining the filaments, yarns,ribbons, sheetsor the like from any substantial reduction in lineardimensions, and in the case of ribbons and sheets, planar dimensions.The following specific examples are illustrative of the details of theinvention. It is to be understood that the invention is not limited tothe details set forth therein.

Example I A 45-denier, -filament polyhexamethylene adipamide yarn, colddrawn 410% with a Z twist of turns per inch, was wound under a tensionof 10 grams, on an aluminum bobbin having a four-inch diameter. Thebobbin was then placed in a steam chamber, subjected to saturated steamat 120 C. for 20 minutes and the yarnthen removed from the bobbin. Thissteamtreatment of the wound yarn set the yarn without noticeablyshrinking the same. The residual shrinkage of the treated yarn wasdetermined and found to be 1% as compared with a residual shrinkage ofthe untreated yarn of 7%.

Example II A 45-denier, 15-filament polyhexamethylene adipamide yarn,drawn 376% having a twist of 4.5 turns per inch, was wound on a bobbinin the same manner as described in Example I, and was set by submergingthe same in boiling water for five minutes. The residual shrinkage ofthe resultant yarn was 4% as compared with a residual shrinkage of theuntreated yarn of 10.2%.

Example III A woven fabric was constructed using 140 threads per inch of-denier, 10-filament, 10-

turn 8 twist dull yarn of oriented polyhexamethylene adipamide as thewarp, and 120 threads per inch of 35-denier, 10-filament, 10-turn Stwist dull yarn of oriented polyhexamethylene adipamide in the filling.A portion of this fabric was tightly stretched on'a tentering frame andheld against substantial shrinkage while subjecting the same to theaction of saturated steam at C. for 15 minutes. A sample of this fabricwhen subjected to the conditions used in determining residual shrinkageof a yarn and measured in the warp and filling direction will be foundto shrink approximately 1%. A sample of a similar untreated fabric whentested in the same manner will be found to shrink approximately 5%.

Example IV strain against reduction in linear dimension and placed in anautoclave and subjected to saturated steam at a pressure of '70 poundsper square inch for 30 minutes. The properties of the treated monofilwere determined and found to be: denier, 13,800; tenacity (gramsperdenier) 3.7; tensile strength (pounds to break) elongation (to break)20%. The residual shrinkage was less than 0.5%.

The invention may be practiced continuously by subjecting the yarn tohot-wet treatments while running continuously between rolls running atthe same peripheral speed and gripping the yarn so that it cannotshrink. Such treatments may also be applied to ribbons, sheets, andwoven fabrics in the same manner. Proper provisions may be made toprevent lateral shrinkage as by gripping belts, etc. The yarn can betreated withhot water or steam either at atmospheric or superatmosphericpressures. the yarn or fabric may travel will depend on the length ofthe length of the chamber in which the treatment is applied, thetemperature of the setting agents and the reduction in residualshrinkage desired. The higher the temperature of the treatment and thelonger the travel of the yarn, the higher the speed of travelpermissible to maintain the same reduction in residual shrinkage.

While in the foregoing examples this invention has been illustrated byhot-wet treatments involving hot water or steam it is not so limited.Organic non-solvent swelling agents for the polyamides are also useful.These may be hydroxylated compounds such as the aliphatic alcohols.Methanol, isopropanol and isobutanol are particularly'useful. Otherhydroxyl-containing compounds which are useful include ethyl lactate,dimethyl tartrate, ethyl glycolate, ethanolamine, diacetone alcohol andpolyhydric alcohols; e. g., ethylene glycol and glycerol. Usefulcompounds which do not contain the hydroxyl group include organic aminessuch as aniline, toluidine, dibutyl amine, etc., as well as nitriles andamides. The

The speed at which use of dilute aqueous solutions of alkali metalsulfltes; e. g. sodium sulfite, is particularly effective. The onlyrequirement of agents used according to this invention is that they havea swelling action on the polyamides without dissolving them; that is,they are substantially chemically inert towards polyamides. Thisrequirement for a non-solvent, organic swelling agent may be satisfiedby a mixture of a solvent and a non-solvent. Setting agents which areeffective produce at least 1% increase in the length of the unorientedfilament at 25 C. and preferably They should also be tested at thesetting temperature to be sure they are not active solvents.

While any hot-wet treatment has a setting action on oriented polyamidearticles, it is generally preferred to employ temperatures between 65 C.and 175 C. for periods of a few minutes to an hour. In order to obtainthe advantages of the present invention the setting treatment should becarried out at such a temperature and for such a period of time as toreduce the residual shrinkage of the polyamide structures at least to75% of that of the unset structure. The temperature and period oftreatment depend upon the particular polyamide and its physical form andupon the setting agent employed. Generally, the higher the temperatureemployed the shorter the period that is necessary. The degree of settingin a given time is roughly a linear function of temperature. Forexample, the preferred temperature range for water and saturated steamis 95 C. to 110 C. for times ranging from one to fifteen minutes. Atreatment for one minute with saturated steam is approximatelyequivalent to a five minute treatment with hot water at 95 C. Similarly,a five minute treatment with methanol vapor at 100 C. produces as muchsetting as thirty minutes liquid treatment at 65 C.

Dry heat is ineffective as an agent to substantially reduce residualshrinkage where the polyamide structure is held against shrinkage inaccordance with the present invention.

. While this invention has been described with particular emphasis onyarns consisting solely of oriented linear polyamide filaments, it isalso applicable to mixed textile materials. Similarly, yarns comprisingstaple length polyamide filaments alone or in combination with othertextile Likewise, mixed fabrics may be treated according to thisinvention. This invention is also appliable to oriented polyamidefilaments, yarns and the like comprising modifying agents, for eX-ample, luster-modifying agents, delusterants, etc.

The process of this invention may also be practiced to advantage onarticles made from other synthetic linear polymers such as thepolyesters.

etc., described in U. S. Patent No. 2,071,251, as

well as articles made from polyester-amide interpolymers.

The setting of polyamide structures in accordance with the presentinvention can be definitely discerned in the set structures. The settingtreatment changes the crystalline characteristics of synthetic linearpolyamide structures as evidenced by X-ray investigation. The X-raydiffraction patterns which change markedly upon cold drawing become muchsharper after the yarn is subjected to the setting treatments of thisinvention. By X-ray investigation it can therefore be definitelyascertained whether or not a structure has been subjected to the processofthis invention.

By the practice of this invention it is possible to produce,continuously or discontinuously, oriented polyamide filaments, yarns,and the like having a uniformly low residual shrinkage by I treatmentwhereby the linear dimensions or the yarn are not materially reduced. Itis therefore possible to produce woven fabrics and the like which willnot shrink appreciably upon subsequent treatment with hot water, steamor other non-solvent swelling agents for the. polyamides and in whichthe structure of the fabric is not injured by shrinking treatment. Yarnstreated in accordance with this invention can also be used for theproduction of knitted fabrics which will not shrink appreciably in hotwater, steam, and the like. Furthermore, the same treatments which areused to remove the residual shrinkage when applied to fabrics impart tothem substantially permanent crease resistance. Since it is possible toreduce the residual shrinkage without undergoing shrinkage, there is noloss of length so that the yarns produced can be used more eflicientlyand effectively than those produced by other processes.

Since it is obvious that many changes and modifications can be made inthe details of the invention above set forth, it is to be understoodthat the invention is not to be limited except as set forth in theappended claims.

I claim:

1. In a process for reducing the residual shrinkage of orientedsynthetic linear polyamide structures of filaments, yarns, ribbons,sheets and woven fabrics the construction of which will permitprevention ofshrinkage of filaments and yarns 'of which they are made,the step which comprises setting said structures by treating the samewith a non-solvent swelling agent for the polyamide at a temperature ofbetween C. and 175 C. for a sumcient period of time to reduce theresidual shrinkage of the structure at least to of that of a similarunset structure while preventing substantial reduction in dimension ofsaid structures.

2. In a process for reducing the residua. shrinkage of orientedsynthetic linear polyamide structures of filaments, yarns, ribbons,sheets and woven fabrics the construction of which will permitprevention of shrinkage of filaments and yarns of which they are made,the step which comprises setting said structure by treating the samewith a non-solvent swelling agent for the polyamide at a temperature ofbetween 65 C. and C. for a period of l to 15 minutes while preventingsubstantial reduction in dimension of said structures.

3. In a process for reducing the residual shrinkage of woven fabric theconstruction of which will permit prevention of shrinkage of filamentsand yarns of which it is made and in which said filaments and yarns arecomposed of oriented synthetic linear polyamides which comprisessubjecting said yams and filaments to a setting treatment with anon-solvent swelling agent for the polyamide at a temperature of 65 C.to 175 C. for a period of 1 to 15 minutes while preventing substantialreduction in linear dimension of said filaments and yarns.

4. In a process for reducing the residual shrinkage of filaments andyarns composed of oriented synthetic linear polyamides which comprisessetting said filaments and yarns by treating the same with a non-solventswelling agent for the polyamide at a temperature of 65 C. to 175 C. fora period of 1 to 15 minutes while preventing substantial reduction inlinear dimension oiv said filaments and yarns.

5. In a process for reducing the residual shrinkage of filaments andyarns composed of oriented synthetic linear polyamides which comprisescontinuously setting said filaments and yarns by treating the same witha non-solvent swelling agent for the polyamide at a temperature of 65 C.to 175 C. for a period 01 1 to 15 minutes while preventing substantialreduction in linear dimension of said filaments and yarns.

6. In a process for reducing the residual shrinkage of sheets andribbons composed of oriented synthetic linear polyamides which comprisessetting said sheets and ribbons by. treating the same with a non-solventswelling agent for the polyamide at a temperature 01' 65 C to JOHN B.MILES.

